Hardened sites were built with great urgency beginning in the late 1950s, upon the advent of intercontinental ballistic missiles (ICBMs). Hardened sites were also designed to protect key command and control centers. The most common hardened sites are underground silos, covered with many feet of concrete and topped with massive steel doors. These silos contain intercontinental nuclear-tipped missiles. Command centers for the silos are also hardened. In case of a first strike by the adversary, the hardened missile silos—at least in theory—would protect the site, thereby allowing the nation under attack to launch a credible counterstrike.
Typical of hardened sites is the now-decommissioned Atlas E missile site outside Wamego, Kansas, which was constructed in the mid-1960s and designed to withstand a direct nuclear hit. Deep underground are 16,000 square feet housing the command center, several elevators, living quarters, bathrooms, a kitchen, and recreational facilities. The site contained large stores of food, water, clothing, and medical supplies so that the crew could live underground without additional assistance for a prolonged period. The site was also outfitted with its own electrical generation system and air purification apparatus designed to filter out chemical and biological agents as well as radioactive contamination.
Air bursts are ineffective against hardened sites, which may only be attacked by ground burst nuclear weapons, usually smart bombs aimed to strike the very door of the missile silo and then penetrate and explode. Some hardened sites are currently so deep underground that existing weapons cannot disturb them.
Spencer C. Tucker
Sagan, Scott D. Moving Targets: Nuclear Strategy and National Security. Princeton, NJ: Princeton University Press, 1990.; United States Bureau of Naval Personnel. Principles of Nuclear Missiles and Guided Weapons. Washington, DC: U.S. Government Printing Office, 1972.